The usual progression is start working as an apprentice and then as a plumber for a larger agency, then on your own, then you become the larger agency and hire assistants and other plumbers, then you “retire”. The latter part can be quite lucrative.

This is like saying you can make billions as a software developer, when in reality you’re talking about a startup founder with a software business.

Yes.... but that's running a company, not being a plumber lol!

It's very important to distinguish that stuff, because as we saw in The Millionaire Next Door you can often end up classifying someone as "electrician" or "plumber" when more properly they should be classified as "small business owner".

Not $300k. But healthy $200k in Midwest is a lot of money.

Yeah I can believe $200k if you're doing commercial stuff running a crew. Unsure how much of that work there is in the Midwest.

No way you're making $200k doing residential work, even in large cities. Definitely not if you aren't on your own.